The field of the invention relates generally to electrostatic precipitators for use in air pollution control, and more specifically to a rapping process for use in cleaning the internal collection plates and discharge electrodes of electrostatic precipitators.
Continuous emphasis on environmental quality has resulted in increasingly strenuous regulatory controls on industrial emissions. One process for use in controlling air pollution facilitates the removal of undesirable particulate matter from a gas stream via electrostatic precipitation. Known electrostatic precipitators electrically charge and collect particulates generated in industrial processes such as those occurring in cement plants, pulp and paper mills, and utilities. For example, the particulate may be negatively charged and attracted to, and collected by, positively charged metal plates. Alternatively, the particulate may be positively charged and attracted to, and collected by, negatively charged metal plates. The cleaned process gas may then be further processed or safely discharged to the atmosphere.
During operation of an electrostatic precipitator, known collector plates, electrodes, and other precipitator internal components may be periodically cleaned to remove any dust build-up that has accumulated on the surfaces of such components. For example, a mechanical rapper can be used to facilitate cleaning of such components. Rappers are electro-mechanical devices that may be used to mechanically dislodge collected particulate/materials within an electrostatic precipitator (an ESP), electronic filter, or dust collector by applying direct current (DC) energization to the rapper.
Known rappers include a hammer that mechanically strikes an anvil coupled to internal components within the ESP. Striking the rapper shaft or anvil with the hammer transmits mechanical forces to these components to dislodge collected materials.
Several rapper variations exist which may be employed in the cleaning process. An electronic controller determines the sequence, intensity, and duration of rapping. Particulate dislodged from the plates falls into collection hoppers at the bottom of the precipitator. For example, one known rapper includes a cylindrical hammer or plunger and solenoid coil (also referred to herein as the rapper coil). In such rappers, the solenoid coil is energized to cause the hammer to be moved vertically to a height above the precipitator surface being cleaned. When the energization is terminated, the hammer strikes the anvil. Another known rapper includes a spring coupled behind the hammer. When the solenoid coil is energized, the hammer compresses the spring against the rapper assembly, and when the energization is terminated, the hammer strikes the anvil. In another known rapper, a spring is coupled behind the hammer. When the solenoid coil is energized the hammer is accelerated towards the anvil.
However, during operation, numerous operational problems associated with the cleaning process may be experienced. For example, excessive rapping may result in the particulate billowing from the plate into the gas stream where it may be re-entrained in the gas flow and discharged from the exhaust stack, thus increasing emissions into the atmosphere. In contrast, insufficient rapping may prevent particulate from being removed from the surfaces to be cleaned. In both situations, as collection efficiency of the precipitator is reduced, the gas volumes that can be treated by the precipitator are also reduced. In most industrial applications there is a direct correlation between precipitator capacity and production capacity. For example, significant monetary benefits may be derived from optimizing rapper efficiency.